Packet data communication is known in cellular telephone systems, as is evidenced by, for example, commonly assigned U.S. Pat. No.: 5,257,257, issued Oct. 26, 1993, entitled "Method of Controlling the Operation of a Packet Switched CDMA Communication Network for Controlling the Operation of Transmitters and Receivers", by X. H. Chen and J. Oksman.
The cellular telephone industry has experienced an explosive growth in the last decade. This growth has driven many communication systems near capacity, particularly in major metropolitan areas. As a communication system's capacity is reached, users experience longer delays. Thus, innovative techniques are required to optimize system throughput and minimize delays.
In conventional circuit switched communication networks, users are offered a traffic channel based on a first-come, first-served basis. If the communication network reaches its maximum capacity, calls are blocked. In order to serve a predicted amount of user traffic while maintaining an acceptable level of blocking, the network must reserve sufficient capacity, i.e. traffic channels. The number of channels reserved to ensure sufficient capacity may be calculated from the Erlang B formula.
In contention based packet data networks, packet data requests are also served on a first-come, first-served basis. However, blocking levels are reduced by setting a limit on the maximum transmitted packet length. Thus, traffic channels are shared by the packet data users in a time multiplexed fashion. As the input load increases within the packet data network, users start to experience longer delays. Rate control for the packet data networks operating in a time multiplexed fashion is straightforward. The efficiency of the packet data network is determined by the speed at which the network allocates and releases traffic channels. Based on the nature of packet data transmissions, packet data networks can be quite stable and efficient, as long as the average input load is below a specified level.
When CDMA networks based on the TIA/EIA/IS-95A, Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, hereinafter simply referred to as IS-95A, offer packet data services they offer circuit switched call setup. Therefore, a CDMA network employing IS-95A can not offer the function of fast traffic channel allocation or releasing as needed for the packet data traffic. Using the conventional circuit switched Erlang B formula, the network is inefficient since the call duration for a packet data transmission is normally much shorter than a switched call.
Thus, a rate control strategy is needed in CDMA networks which improves channel utilization for packet data users while it reduces delays due to blocking.
Objects and Advantages of the Invention
It is a first object and advantage of this invention to provide an efficient technique for transmitting packet data over a cellular communication network that overcomes the foregoing and other problems.
Another object and advantage of this invention is to define techniques of rate control used by a code division multiple access (CDMA) network to control the data rate allocations to packet data users in the network.
Another object and advantage of this invention is to define techniques of rate control used by a CDMA network to optimize total system throughput, minimize user delay, and to offer more user traffic capacity per cell.